Process for production of cyclohexane



The hydroformed product is then hydrogenated catalytically with hydrogen to convert benzene into cyclohexane. Hydrogenation can be operated at temperature from 600 to 800 F. and pressure of 500 to 1000 p. s. i. g., preferably about 700 F. and 700 p. s. i. g. Suitable hydrogenation catalysts are nickel-tungsten sulfide, cobalt molybdate, and molybdena on alumina. The resulting cyclohexane-containing hydrogenation product is freed of hydrogen gas and fractionally distilled to prepare high purity cyclohexane as a bottoms fractions. At least part of the low boilers obtained in the final fractionation can be blended with the hydrocarbon feed mixture for recovery of cyclohexane and methylcyclopentane values.

Advantageously, the quantity of the additional methylcyclopentane-containing mixture (resulting from isomerizing the cyclohexane-enriched fraction) which is recycled to form a blend with the hydrocarbons fed to the primary methylcyclopentane stripping operation is controlled to establish and maintain mol ratio of cyclohexaneztotal associated hydrocarbons in the resulting blend, exclusive of methylcyclopentane, not substantially below about 0.05 :l and preferably above about 0.111. By so regulating this recycle the eliciency' and economy of the subsequent steps, i. e. the fractional distillation and the catalytic isomerization of the cyclohexane-enriched fraction, is substantially increased.

The drawings are flow diagrams showing ways of operating our process. Pumps, compressors, and controllers of flow, temperature, and pressure (not shown), are supplied where necessary or desirable. The specific example below is described with particular reference to the Figure l. All percentages are mol percentages and all parts are mol parts unless otherwise specified.

Example 3700 parts of straight run naphthenic distillate from California petroleum having boiling range of about 158 to 225 F. at atmospheric pressure and containing 5% light ends, cyclohexane, 10% methylcyclopentane, and balance of associated hydrocarbons is fed through lines 9 and 10 into fractionating tower 11 wherein hydrocarbons having atmospheric boiling point below 160 F. are separated and withdrawn through line 12. Thus stripped, the remainder of the naphthenic distillate, 3515 parts, is withdrawn through line 13. The stripped remainder is passed through line 14 into fractionating tower 15 together with 750 parts recycle hydrocarbons from line 25, obtained as hereinafter described. A methylcyclopentane cut, 640 parts, having boiling point range at atmospheric pressure at 160-170" F., is withdrawn through line 16. The residue consisting of cyclohexane and other higher boiling hydrocarbons is withdrawn through line 17 and passed into fractionating tower 18 wherein 3625 parts of a mixture of cyclohexane and associated hydrocarbons (principally mixed heptanes) having atmospheric boiling point between 170 and 200 F. is separated and withdrawn through line 20, heated in exchanger 21, and passed through line 22 into catalyst case 23. High boiling residue, 2625 parts, is withdrawn from tower 18 through line 19.

Catalyst case 23 is packed with cobalt on HF-treated alumina. Flow thereover is maintained at liquid space velocity of 0.5 volume per volume of catalyst. Temperature of this operation is maintained at 850 F. and average pressure of 1500 p. s. i. g. whereby the major portion of the cyclohexane in the mixture is converted into additional methylcyclopentane. The catalytically treated mixture, 1000 parts, is withdrawn through line 24. A quarter of it is sent to fractionating tower 27 through line 26. The remainder is recycled through line for subsequent separation in tower 15. The resultant composition fed to tower 15, formed by the mixing of the stripped naphthenic distillate and said recycled remainder, has ratio of cyclohexanezassociated hydrocarbons exclusive of methylcyclopentane of about 0.124:1.

In tower 27 additional catalytically-formed methylcyclopentane, parts, is stripped from said quarter of the catalytically treated mixture, and the higher boiling materials are purged from line 29. The 90 parts of the additional catalytically-formed methylcyclopentane are withdrawn through line 28, combined with that flowing in line 16, and this blend passed through line 31 into catalyst case 33 with recycled hydrogen owing in from line 32 from a source described hereinafter.

Catalyst case 33 is packed with platinized HF-treated alumina pellets and conditions therein are: temperature of 875 F.; pressure of 500 p. s. i. g.; and liquid space velocity of 3.0 volumes per volume of catalyst per hour, whereby preponderantly benzene and hydrogen are formed from the methylcyclopentane fed. The mixture is conducted from catalyst case 33 through line 34 and mixed with additional hydrogen, 600 parts, entering inlet 3S. The combined flows are then passed into hydrogenator 36, packed with tungsten sulfide-coated alumina pellets. Conditions of hydrogenation are 600 F., 1000 p. s. i. g., and liquid space velocity (exclusive of hydrogen) of 0.5 volume per volume of catalyst per hour whereby the catalytically-formed benzene is substantially entirely converted into cyclohexane.

The hydrogenation product is withdrawn through line 37, condensed in exchanger 38, and passed through line 39 into vessel 40. Gaseous hydrogen is separated and recycled through line 32 as previously described with a hydrogen purge being taken 01T line 47. Separated liquid is passed through line 41 into fractionating tower 42 wherein parts of hydrocarbons having boiling point below cyclohexane are fractionally distilled and withdrawn from line 43. A purge fraction of this distillate can be withdrawn from line 45, and the remainder can be recycled to blend with the straight run naphtha feed entering line 9. From line 46 there is withdrawn purified hydrogenation product containing 590 parts cyclohexane.

The operations depicted in Figure 2 are similar to those of Example 1 and use essentially the same equipment items as are shown in Figure l except that: the entire isomerized mixture from catalyst case 23 is passed into tower 27 for fractionation instead of being recycled in part to tower 15; catalytically-formcd additional methylcyclopentane is stripped in tower 27 and withdrawn through line 28 while the bulk of the resulting residue is recycled through line 48 into exchanger 21 for isomerization processing; and sufficient purge of the resulting residue is withdrawn from tower 27 by line 29 to prevent reduction of the mol ratio of cyclohexanezother hydrocarbons in the isomerization reactor feed to a value below about 0.1:1.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for production of cyclohexane comprising: forming a feed mixture of a petroleum distillate having boiling point range between about and about 225 F., said petroleum distillate containing methylcyclopentane, cyclohexane, and associated hydrocarbons with the ratio of lcyclohexane to said associated hydrocarbons above about 0.1:1, and a portion of recycled isomerization reaction product containing additional catalytcallyformed methylcyclopentane and unreacted cyclohexane, said portion being obtained from a later stage of the process and its quantity being regulated for maintaining the ratio of cyclohexane to associated hydrocarbons in said feed mixture at a value above about 0.1:1; stripping a methylcyclopentane-rich fraction having boiling point range between about 160 and about 170 F. from said feed mixture, thereby leaving a liquid residue containing cyclohexane together with associated hydrocarbons;

stripping a cyclohexane-enriched distillate from said residue; isomerizing the major fraction of cyclohexane in said cyclohexane-enriched distillate into additional methylcyclopentane by contacting said cyclohexane-enriched distillate in vapor phase with an isomerization catalyst at a temperature of SOO-900 F. and a pressure of SOO-2000 p. s. i. g.; recycling a fraction of the isomerization reaction product into admixture with said petroleum distillate for forming said feed mixture; recovering additional catalytically-formed methylcyclopentane from the balance of the isomerization reaction product; conducting the recovered additional catalyticallyformed methylcyclopentane, the methylcyclopentane previously stripped from the feed mixture, and hydrogen into contact with a hydroforming catalyst at a temperature maintained between 840 and 980 F. and a pressure between 250 and 500 p. s. i. g., thereby reforming methylcyclopentane into benzene and hydrogen; converting said benzene into a cyclohexane-containing hydrogenation product by catalytic hydrogenation with hydrogen at a temperature from 600 to 800 F. and a pressure of 500 to 1000 p. s. i. g.; and fractionally distilling cyclohexane from the resulting hydrogenation product.

2. A process for production of cyclohexane comprising: forming a feed mixture of a petroleum distillate having boiling point range between about 160 and about 225 F., said petroleum distillate containing methylcyclopentane, cyclohexane, and associated hydrocarbons with the ratio of cyclohexane to said associated hydrocarbons above about 0.1:1, and a portion of recycled isomeriza- 30 ation reaction product containing additional catalyticallyformed methylcyclopentane and unreacted cyclohexane, said portion being obtained from a later stage of the process and its quantity being regulated for maintaining the ratio of cyclohexane to associated hydrocarbons in said feed mixture at a value above about 0.1:1; stripping a methylcyclopentane-rich fraction having boiling point range between about 160 and about` 170 F. from said feed mixture, thereby leaving a liquid residue containing cyclohexane together with associated hydrocarbons; stripping a cyclohexane-enriched distillate from said residue; isomerizng the major fraction of cyclohexane in said cyclohexane-enriched distillate into additional methylcyclopentane by contacting said cyclohexane-enriched distillate in vapor phase with an isomerization catalyst at a temperature of 80G-900 F. and a pressure of 500-2000 p. s. i. g.; recycling a fraction of the isom'- erization reaction product in to admixture with said petroleum distillate for forming said feed mixture; recovering additional catalytically-formed methylcyclopentane from the balance of the isomerization reaction product; and converting the recovered additional catalyticallyformed methylcyclopentane and the methylcyclopentane previously stripped from the feed mixture into cyclohexane.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PRODUCTION OF CYCLOHEXANE COMPRISING: FORMING A FEED MIXTURE OF A PETROLEUM DISTILLATE HAVING BOILING POINT RANGE BETWEEN ABOUT 160* AND ABOUT 225*F., SAID PETROLEUM DISTILLATE CONTAINING METHYLCYCLOPENTANE, CYCLOHEXANE, AND ASSOCIATED HYDROCARBONS WITH THE RATIO OF CYCLOHEXANE TO SAID ASSOCIATED HYDROCARBONS ABOVE ABOUT 0.1:1,AND A PORTION OF RECYCLED ISOMERIZA-TION REACTION PRODUCT CONTAINING ADDITIONAL CATALYTICALLYFORMED METHYLCYCLOPENTANE AND UNREACTED CYCLOHEXANE, SAID PORTION BEING OBTAIN FROM A LATER STAGE OF THE PROCESS AND ITS QUANTITY BEING REGULATED FOR MAINTAINING THE RATIO OF THE CYCLOHEXANE TO ASSOCIATED HYDROCARBONS IN SAID FEED MIXTURE AT A VALUE ABOVE ABOUT 0.1:1, STRIPPING A METHYLCYCLOPENTANE-RICH FRACTION HAVING BOILING POINT RANGE BETWEEN ABOUT 160* AND ABOUT 170*F. FROM SAID FEED MIXTURE, THEREBY LEAVING A LIQUID RESIDUE CONTAINING CYCLOHEXANE TOGETHER WITH ASSOCIATED HYDROCARBONS, STRIPPING A CYCLOHEXANE-ENRICHED DISTILLATE FROM SAID RESIDUE, ISOMERIZING THE MAJOR FRACTION OF CYCLOHEXANE IN SAID CYCLOHEXANE-ENRICHED DISTILLATE INTO ADDITIONAL METHYLCYCLOPENTANE BY CONTACTING SAID CYCLOHEXANE-ENRICHED DISTILLATE IN VAPOR PHASE WITH AN ISOMERIZATION CATALYST AT A TEMPERATURE OF 800-900*F. AND A PRESSURE OF 500-2000 P. S. I. G., RECYCLING A FRACTION OF THE ISOMERIZATION REACTION PRODUCT INTO ADMIXTURE WITH SAID PETROLEUM DISTILLATE FOR FORMING SAID FEED MIXTURE, RECOVERING ADDITIONAL CATALYTICALLY-FORMED METHYLCYCLOPENTANE FROM THE BALANCE OF THE ISOMERIZATION REACTION PRODUCT, CONDUCTING THE RECOVERED ADDITIONAL CATALYTICALLYFORMED METHYLCYCLOPENTANE, THE METHYLCYCLOPENTANE PREVIOUSLY STRIPPED FROM THE FEED MIXTURE, AND HYDROGEN INTO CONTACT WITH A HYDROFORMING CATALYST AT A TEMPERATURE MAINTAINED BETWEEN 840* AND 980*F. AND A PRESSURE BETWEEN 250 AND 500 P. S. I. G, THEREBY REFORMING METHYLCYCLOPENTANE INTO BENZENE AND HYDROGEN, CONVERTING SAID BENZENE INTO A CYCLOHEXANE-CONTAINING HYDROGENATION PRODUCT BY CATALYTIC HYDROGENATION WITH HYDROGEN AT A TEMPERATURE FROM 600* TO 800*F. AND A PRESSURE OF 500 TO 1000 P. S. I. G., AND FRACTIONALLY DISTILLING CYCLOHEXANE FROM THE RESULTING HYDROGENATION PRODUCT. 